Geological Structures

Dr. Ahmad Redaa

2025-02-11

Definition of Geological Structures

Forces Acting on Rocks

Source: Steven, E. (2015)

Stress vs. Strain

Types of Tectonic Forces:

  1. Tension → Stretches rocks apart.
  2. Compression → Pushes rocks together.
  3. Torsion → Twisting forces.
  4. Shear → Sideways motion.

Types of Deformation

Source: Steven, E. (2015)
  1. Elastic Deformation → Temporary, rocks return to original shape.
  2. Plastic (Ductile) Deformation → Permanent bending.
  3. Rupture (Brittle) Deformation → Rocks break (faulting).

Classification of Geological structures

Primary Structures

Secondary Structures

Folds

Definition:

Fold Geometry:

Source: Steven, E. (2015)

Types of Folds

Source: https://britannica.com

Based on Symmetry:

Source: https://britannica.com

Based on Limb Inclination:

Source: https://britannica.com
Source: https://slideplayer.com

Based on Fold Axis:

Source: https://all-geo.org

Other Fold Structures

Faults

Definition:

Source: https://www.researchgate.net

Fault Geometry:

Classification of Faults

Source: https://www.pinterest.com
  1. Dip-Slip Faults:
    • Normal Fault → Hanging wall moves down (due to tension).
    • Reverse Fault → Hanging wall moves up (due to compression).

Classification of Faults

Source: https://geo.libretexts.org
  1. Strike-Slip Faults:
    • Left-Lateral → Opposite side moves left.
    • Right-Lateral → Opposite side moves right.

Classification of Faults

  1. Other Faults:
    • Thrust Fault → Low-angle reverse fault.
    • Transform Fault → Large-scale strike-slip fault (e.g., San Andreas Fault).
    • Oblique Fault → Combination of dip-slip and strike-slip motion.
    • Graben Fault → Down-dropped block between two normal faults.

Evidence of Faults

Joints

Source: https://www.nps.gov

Definition:

Formation:

Types of Joints:

Unconformity

Definition:

Types of Unconformities:

Source: https://geologyscience.com
  1. Angular Unconformity → Tilted or folded rocks overlain by flat layers.
  2. Nonconformity → Igneous/metamorphic rocks overlain by sedimentary rocks.
  3. Disconformity → Parallel sedimentary layers with an erosional gap.

Evidence of Unconformity: